The unnamed city in Seven is a depressing place. It's gray and gloomy. The weather forecast for the next week calls for a 100 percent chance of rain and scattered serial killings. But Detective Somerset doesn't know about the serial killer when the movie begins—just the rain. Before John Doe strikes, Somerset is simply a tired cop ready for retirement.
Call to Adventure
Somerset is ready to throw in the towel after a long career and retire to a cabin in the woods. He clearly hasn't seen many movies because if he had, he'd know this is the perfect time for his One Last Case. Somerset's last case begins when he finds the corpse of a giant man who appears to have been fed to death … and it's not even Thanksgiving.
Refusal of the Call
Somerset isn't stupid. He knows his One Last Case will be a big one, and he asks to be reassigned. He also doesn't think Mills is experienced enough to handle the case, but the captain denies Somerset's request for transfer.
Meeting the Mentor
In this case, Somerset is the mentor to Mills. Somerset is cool and collected to counter Mills' hotheaded impulsiveness. Somerset uses the resources he has earned during his years on the force to help the younger detective. Because Somerset knows he will be leaving, he needs to groom his replacement.
Crossing the Threshold
When Mills' greed case prompts Somerset to go back to the original crime scene, he finds the word "gluttony" written on the wall. The cases are linked. Somerset knows there is no turning back here.
Tests, Allies, Enemies
Mills and Somerset slowly get closer to John Doe. Their tests come in the form of the seven deadly sins. Each crime is more twisted and gruesome than the one before it, and the detectives must work together to find Doe's true identity and stop him before he kills again.
Approach to the Inmost Cave
Somerset uses the library to find a man whose reading records are filled with references to the seven deadly sins. (Yes, the library knows you've read every Nicholas Sparks novel. Twice.) This leads the detectives to John Doe's apartment, which is the creepiest man cave ever. It is packed with notebooks full of crazy writing and photos of his crime scenes. The only thing it's lacking is the man itself.
After finding Doe's apartment, the detectives still don't have Doe himself. His next series of gruesome crimes is more of an ordeal for his victims than it is for the detectives. But each time Doe kills, the detectives fear he is slipping through their fingers and that they may never catch him.
Reward (Seizing the Sword)
The reward for any criminal detective is catching the killer. John Doe turns himself in, which isn't that rewarding. It would be like running 25.9 miles of a marathon, but then someone picks you up at the very end and carries you over the finish line. By subverting the seizing of the reward, Doe ensures that control remains in his hands.
Of course, it turns out that having him in custody isn't a reward at all. It's part of his master plan.
The Road Back
The detectives drive a literal road into the desert, where Doe says he has hidden one final victim. Mills is cocky because he has Doe in custody. But Somerset is suspicious that the road will lead to even more trouble, rather than closure.
The climax occurs when Doe presents Mills with a brown paper package tied up with string. It's one of his favorite things: the head of Mills' wife. Here, Mills must make a big decision: shoot and kill Doe or swallow his wrath. Either way, Doe wins. There is no way to bring his wife back, but Mills pulls the trigger anyway, ending Doe's life and his own career.
Return With the Elixir
Somerset retires, but what should be a cause for celebration and relaxation is tainted by the evilness of John Doe's crimes. Somerset finds no solace in retirement. Instead, he has lots of free time on his hands to ruminate on the evil nature of mankind.
What a happy ending.